Although it is not my intention to give a detailed description of the process of intestinal digestion, it might still be useful briefly to discuss the further fate of the chyme. On the entrance of the chyme into the duodenum, it is subjected to the influence of the bile and pancreatic juice, which are there poured out and also to that of the intestinal secretion. All these secretions have a more or less alkaline reaction, and through their admixture with the chyme its acidity becomes less and less, until at length, at about the middle of the small intestine, the reaction becomes alkaline and continues so as far as the ileo-caecal valve.

Of the bile we know that it has a strongly alkaline reaction and that it is able to emulsify fats. It also possesses antifermentative and slightly purgative properties.

The importance of the liver, however, cannot be judged from the influence which the bile exerts upon the digestive economy. "To regard the liver in this light," says L. Brunton,1 "is just about as rational as to think that an Atlantic steamer has been built for the express purpose of throwing out from its sides the two jets which are formed by the waste water from the engines. The condensed steam may be utilized and so may the bile, but the condensation of steam is not the main object of an Atlantic steamer, nor is the secretion of bile a chief function of the liver".

All the blood from the stomach and intestines must pass through the portal vein before it can reach the general circulation. The hepatic tissue acts the part of a prudent porter at a gate, and turns back or destroys dangerous intruders. The liver serves, briefly, the four following purposes:

1. It is a kind of store-room of the organism, many substances taken up by the digestive process being kept there until their final use in the system. Thus many of the peptones and the greatest part of sugar are stored up in the liver as glycogen.

2. It excludes from the circulation several poisonous matters or destroys them; curare, for instance, which is so poisonous when injected into the blood, proves quite innocuous when taken by the mouth, the reason being that the liver does not pass this poisonous matter into the circulation but retains it, and finally excretes it through the bile. The liver guards the organism from the entrance of many detrimental substances.

1 T. L. Brunton: "Disorders of Digestion," London, 1893.

3. It has also been proven lately that the liver is the main place where urea is formed.

4. The Secretion Of Bile

If now we return to the subject of intestinal digestion, we shall have to speak, firstly, of the pancreatic secretion, which is the most energetic and general in its action of all the digestive juices. It unites in itself the action of the saliva and the gastric juice besides having properties of its own. By means of its trypsin ferment, it converts albuminous bodies into peptones, but in a much shorter time than the gastric juice. If the action of the pancreatic juice upon albumin goes on for a longer period of time, then leucin, tyrosin, and several other derivatives, as asparaginic acid and hypoxantbin1 are formed. Its diastatic ferment converts starch into sugar and acts in the same way as ptyalin, only more intensely. The third ferment it contains is steapsin, which emulsifies fats and tends to split them up into fatty acids and glycerin. The chemical formula for this process may be expressed as follows:

Tristearin Steapsin Water Glycerin Stearinic acid C2H4(C17H24 - COOH)3 + 3HO2 = C3H5(OH3)+C17H35 - COOH)2

The pancreatic juice acts in an alkaline medium, and the chyme after its entrance into the small intestine is rendered alkaline by the conjoint action of the bile, the pancreatic juice itself, and the enteric juice. The latter, the juice secreted by the small intestine, is known to dissolve only fibrin, but it is yet uncertain whether it contains a diastatic ferment.

1 See C. A. Ewald: "Die Lehre von der Verdauung," p. 176, Berlin, 1890.

The substances that have been left undigested in the stomach are quickly changed into soluble products in the small intestine (chyle) and taken up by the lymphatics and the venous blood current. The principal part of absorption is performed in the small intestine. The chyle has a slightly alkaline reaction until it enters the large intestine, where it again is rendered acid by some of the products of decomposition generated in the lower part of the small intestine. In their passage along the large intestine the undigested materials assume a more solid consistence in consequence of the absorption of the fluid portion, and become gradually changed into faeces and are expelled by the rectum. Several products of proteid decomposition are formed in the large bowel. One of these, discovered by Brieger,1 is called skatol (C9H9N), to which the offensive smell of the faeces is principally due.

1 Brieger: "Ucher die fluchtigen Bestandthcile der nienschlichen Excremcnte." Journal fur prakt. Chernie, 1877.